Java 8 Map not being sorted by value properly

Question

I've read many questions regarding Java 8 and Collections on this site and, given my limited understanding of java streams, I'm having some trouble trying to sort this Map. My code is as follows, being tradeList an ArrayList();

Map<String, Double> buyReport = tradeList.stream().filter(trade -> trade.getInstruction() == Instruction.BUY)
                .sorted(Comparator.comparing(trade -> trade.getInstructionDate()))
                .collect(Collectors.groupingBy(trade -> dateFormat.format(trade.getInstructionDate()),
                        Collectors.summingDouble(trade -> trade.getUSDAmount())));

Does it make any sense to include the .sorted() statement when composing a HashMap? I tried to create a LinkedHashmap, use a custom comparator for the value i need the object instances to compare (a Double), but to no avail.

I can include any other piece of code you may find useful.

Thanks in advance!!

Update: tried this recently; still getting results unordered when grouping by company code and then summing company totals:

Map<String, Double> entityOutgoingReport = tradeList.stream()
                .filter(trade -> trade.getInstruction() == Instruction.SELL)
                .collect(Collectors.groupingBy(trade -> String.valueOf(trade.getEntity()),
                        LinkedHashMap::new,
                        Collectors.summingDouble(trade -> trade.getUSDAmount())));

for (String entity : entityOutgoingReport.keySet()) {
            String key = entity;
            String value = decFormat.format(entityOutgoingReport.get(entity));
            tableBuilder.addRow(key, value); //Just pretty printing to console
        }

first sort, then collect to map... order is of course broken — Eugene, Mar 29 '18 at 15:40
@HadiJ I will try that. I will still need to summarize data in the array list, so as to have daily totals for a particular company. I'll let you know — Juan M, Mar 29 '18 at 15:48

Ousmane D. · Accepted Answer · 2018-03-29T16:00:56.540

0

Simply supply a LinkedHashMap into which the results will be inserted therefore maintaining order.

.collect(Collectors.groupingBy(trade -> 
       dateFormat.format(trade.getInstructionDate()),
                LinkedHashMap::new,
                    Collectors.summingDouble(trade -> trade.getUSDAmount())));

Full code:

Map<String, Double> entityOutgoingReport = 
      tradeList.stream()
               .filter(trade -> trade.getInstruction() == Instruction.SELL)
               .sorted(Comparator.comparing(trade -> trade.getInstructionDate()))
               .collect(Collectors.groupingBy(trade -> String.valueOf(trade.getEntity()),
                        LinkedHashMap::new,
                        Collectors.summingDouble(trade -> trade.getUSDAmount())));

edited Mar 29 '18 at 16:00

answered Mar 29 '18 at 15:45

Ousmane D.

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I'm sorry i edited my question to make it more readable. Still getting unordered results when printing – Juan M Mar 29 '18 at 15:56
@JuanM why are you removing sorted?? – Ousmane D. Mar 29 '18 at 15:57
@JuanM you're not going to have it sorted if you remove the call to `sorted`.. see edit. – Ousmane D. Mar 29 '18 at 16:01
This is the right answer, thanks so much (y) – Juan M Mar 29 '18 at 16:39

Java 8 Map not being sorted by value properly

1 Answers1